feat(admin): Add activity logs page and fix AI chat markdown rendering

- Add paginated activity logs API with filters (date, module, action, keyword)

- Add ActivityLogsPage with table, filters, and detail modal

- Add markdown rendering support for AI chat messages

- Remove prototype placeholder content from chat sidebar

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-v2/src/framework/layout/AdminLayout.tsx

@@ -13,6 +13,7 @@ import {
   MenuUnfoldOutlined,
   BellOutlined,
   BookOutlined,
+  FileTextOutlined,
 } from '@ant-design/icons'
 import type { MenuProps } from 'antd'
 import { useAuth } from '../auth'
@@ -94,6 +95,11 @@ const AdminLayout = () => {
       icon: <TeamOutlined />,
       label: '租户管理',
     },
+    {
+      key: '/admin/activity-logs',
+      icon: <FileTextOutlined />,
+      label: '运营日志',
+    },
     {
       key: '/admin/users',
       icon: <UserOutlined />,